|Description||6/4-Bit VID Programmable Current DAC for Point of Load Regulators with Adjustable Start-Up Current|
|LM10011SDX/NOPB Datasheet PDF : 24 Pages |
SNVS822A – DECEMBER 2012 – REVISED NOVEMBER 2014
7.3 Feature Description
The LM10011 can be treated as a D/A converter, converting digital VID codes to analog outputs. The LM10011
DAC analog output is a current that flows out of the IDAC_OUT pin. The IDAC_OUT pin is intended to be
connected to the feedback node of a voltage regulator as shown in Figure 11. In a typical voltage regulator, the
current in RFB2 is constant by virtue of the regulator feedback loop maintaining the reference voltage at the
feedback node. The current flowing through RFB2 is the same current flowing through RFB1. When current is
injected into the feedback node by the LM10011, less current is required from the RFB1 resistor. The
consequence of this is that the output voltage of the regulator will decrease to maintain the total amount of
current in RFB2 to regulate at the correct feedback (reference) voltage.
Each VID code corresponds to a different IDAC_OUT current and thus a different output voltage. Increasing the
VID code lowers the IDAC_OUT current and raises the output voltage. Decreasing the VID code raises the
IDAC_OUT current and lowers the output voltage. All VID codes are decoded into a 6-bit or 4-bit current DAC
output whether the MODE equals 0 (connected to GND) or 1 (connected to VDD), respectively.
- +- VOUT
Figure 11. Output Voltage (VOUT) is Controlled Via Current Injection into the Feedback Node
7.3.1 Current DAC
The LM10011 current DAC is based on a low-voltage bandgap reference setting a current through a precision
adjustable resistor. This bandgap is trimmed for precision and gives excellent performance over temperature.
The output current has a maximum full-scale range [VID = 000000b] of 59.2 µA and is adjustable with a 6- or 4-
bit VID word. This allows for 64 or 16 settings with a resolution of 940 nA or 3.76 µA, respectively. The current
DAC also has a slew limit to prevent abrupt changes in the output. The slew limit is represented as a time
constant, t6 = 40 µs, in the Electrical Characteristics table. A deglitch filter for the VID inputs provides noise
immunity and effectively adds a small delay from the transition of a VID line to the change in IDAC_OUT current.
7.3.2 Enable Pin and UVLO
The enable (EN) pin allows the output of the device to be enabled or disabled (IDAC_OUT = 0.0 µA) with an
external control signal. This pin is a precision analog input that enables the device when the voltage exceeds
1.34 V. The EN pin has 100 mV of hysteresis and will disable the output when the enable voltage falls below
1.23 V. If EN is not used, it can be left open, and will be pulled high by an internal 2-μA current source. Since the
EN pin has a precise turn-on threshold it can be used along with an external resistor divider network from VDD to
configure the device to turn on at a precise input voltage.
The LM10011 has a built-in undervoltage lockout (UVLO) protection circuit that keeps the device from operating
until the input voltage reaches 2.65 V (typical). The UVLO threshold has 200 mV of hysteresis that keeps the
LM10011 from responding to power-on glitches during start-up. Note that descending below the EN voltage
and/or the UVLO voltage are functionally the same as a reset. Bringing the device back from a low enable setting
or from a VDD UVLO event will reset the IDAC_OUT current to its start-up RSET setting.
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